Grafana is not going beyond login screen when using public domain. On local LAN its working fine

I am using Grafana in my Local LAN and its working perfectly fine. But when I have a routed a public domain to the same server , its not going beyond login screen. IN login screen when I enter uname and password , it shows a message “authenticated” for 1 second and then reload login page again. I have tried each and every suggestion mentioned by community members but still facing same problem.